Function LogicalTapeSetCreate

src/backend/utils/sort/logtape.c:689–738

* Create a set of logical tapes in a temporary underlying file. * * Each tape is initialized in write state. Serial callers pass ntapes, * NULL argument for shared, and -1 for worker. Parallel worker callers * pass ntapes, a shared file handle, NULL shared argument, and their own * worker number. Leader callers, which claim shared worker tapes here, * must supply non-sentinel values for

 * infrastructure that may be lifted in the future.
 */
LogicalTapeSet *
LogicalTapeSetCreate(int ntapes, bool preallocate, TapeShare *shared,
					 SharedFileSet *fileset, int worker)
{
	LogicalTapeSet *lts;
	int			i;

	/*
	 * Create top-level struct including per-tape LogicalTape structs.
	 */
	Assert(ntapes > 0);
	lts = (LogicalTapeSet *) palloc(sizeof(LogicalTapeSet));
	lts->nBlocksAllocated = 0L;
	lts->nBlocksWritten = 0L;
	lts->nHoleBlocks = 0L;
	lts->forgetFreeSpace = false;
	lts->freeBlocksLen = 32;	/* reasonable initial guess */
	lts->freeBlocks = (long *) palloc(lts->freeBlocksLen * sizeof(long));
	lts->nFreeBlocks = 0;
	lts->enable_prealloc = preallocate;
	lts->nTapes = ntapes;
	lts->tapes = (LogicalTape *) palloc(ntapes * sizeof(LogicalTape));

	for (i = 0; i < ntapes; i++)
		ltsInitTape(&lts->tapes[i]);

	/*
	 * Create temp BufFile storage as required.
	 *
	 * Leader concatenates worker tapes, which requires special adjustment to
	 * final tapeset data.  Things are simpler for the worker case and the
	 * serial case, though.  They are generally very similar -- workers use a
	 * shared fileset, whereas serial sorts use a conventional serial BufFile.
	 */
	if (shared)
		ltsConcatWorkerTapes(lts, shared, fileset);
	else if (fileset)
	{
		char		filename[MAXPGPATH];
		workfile_set *work_set;

		pg_itoa(worker, filename);
		work_set = workfile_mgr_create_set("LogicalTape", filename, false /* hold pin */);
		lts->pfile = BufFileCreateShared(fileset, filename, work_set);
	}
	else
		lts->pfile = BufFileCreateTemp("LogicalTape", false);

	return lts;
}

/*
 * Close a logical tape set and release all resources.